CSS Unveils the SDX7 – At Last, a Replacement for the Extremis

Filed under: Home Audio > Speakers



One of the most famous products from the now defunct Adire Audio was their 7” mid known as the Extremis. Featured in the old Exodus Audio kits and available as a separate driver, the Extremis was well known for its powerful low frequency performance (perhaps the most output in a 6.5”/7” driver). Sadly the Extremis is no more, but through this we gained a new and improved performer, the CSS SDX7.

Pics, specs, and details after the break.

Touted as a replacement for the Extremis primarily in 3 way designs, the SDX7 features a long throw motor using the patented XBL^2 method of improving BL linearity. The result is a lot of throw at low frequencies with very low distortion throughout the entire stroke. Like its predecessor, the motor is the backbone of this driver. Being an XBL^2 driver, the inductance and moving mass is naturally lower than that of 7” drivers with comparable linear stroke. Distortion and inductance is lowered even further by an array of 3 copper shorting rings in the motor.


To sweeten the deal, the SDX7 comes with a carbon fiber cone and a copper phase plug, much like CSS’s FR/WR 4.5” drivers. The carbon fiber, again, keeps the moving mass low and improves efficiency. The cast aluminum basket is designed with both low noise and reduced thermal compression in mind.

The final result is an absolutely gorgeous driver with stellar performance as either a dedicated midbass or as a small sub. It is usable in a two-way as well, as long as you can design your crossover around it.

Having been fortunate enough to demo the Extremis and SDX7 side by side for a couple weeks, I think a lot of people will be extremely impressed and satisfied with the SDX7. It is very clean and detailed at low frequencies and the build quality is excellent. Here’s a sneak peak of a future product you’ll be seeing that utilizes the SDX7’s. Thiele/small parameters follow.



Thiele/Small Parameters:
Qts 0.35
Qes 0.41
Qms 2.2
Vas 23.77 L
Cms 1.03 mn/N
Mms 21.91 g
Sd 127.5 sq cm
Re 6.4 ohms
Le 0.75 mH
BL 8.45 TM
Fs 34 Hz
Xmax 11.1 mm
SPL 85 dB/1W/1m
Pe 100 Watts